1. Field of the Invention
The present invention relates to a deflecting electrode for controlling charged particles, a droplet ejection head provided with the deflecting electrode, and a droplet ejection apparatus provided with the droplet ejection head. The present invention relates to inkjet apparatus.
2. Description of the Related Art
Droplet ejection apparatus referred to as continuous apparatus apply continuous pressure to droplets with a pump, push droplets out from nozzles, and additionally apply vibration by vibrating means. In so doing, such droplet ejection apparatus create a state wherein liquid ejected from nozzles forms droplets evenly. Since droplets are continuously ejected from nozzles with this method, it is necessary to sort the droplets used to print according to print data from the droplets that are not used. With a method referred to as the charge deflection method, sorting is conducted by selectively charging droplets, deflecting the droplets with an electric field, and causing the droplets to fly in a trajectory different from that of the non-charged droplets. Sorted non-print droplets are captured by a gutter and collected. In order to realize these functions, a charging electrode, deflecting electrode, and gutter are provided along the droplet flight trajectory from nozzles.
In order to configure an apparatus such that a liquid stream ejected from a nozzle forms droplets, and also such that deflection sufficient for sorting is applied by a deflecting electrode, a certain degree of distance is required from the nozzle to the print medium. For this reason, slight deviations in the angle of droplets ejected from a nozzle greatly affect landing precision. An electrostatic lens is typically known as an electrode configuration that focuses charged particles. An electrostatic lens creates an electric field symmetric about the lens axis by being provided with a plurality of electrodes in the charged particle travel direction. Types of electrostatic lenses may include immersion lens, cylinder lenses, and electrostatic single-lenses, depending on the shape and number of electrodes. A point shared in common by these circularly symmetric electrostatic lenses is that although the focal length changes according to the polarity and charge magnitude of the charged particles, the charged particles converge on the lens axis. In other words, in a typical electrostatic lens, all charged particles converge on the same axis.
In Japanese Patent Publication No. S59-003154 (1984), an electrode group so as to form an electrostatic lens is provided between a charging electrode for charging droplets and a deflecting electrode for sorting, and print droplet trajectory correction is conducted. By arranging electrodes having apertures with the same dimensions and shape along the droplet trajectory, the electrodes manifest the convergence effects described earlier.
Meanwhile, since the electrostatic lens disclosed in Japanese Patent Publication No. S59-003154 (1984) causes charged particles to converge on the lens axis regardless of the charged particle speed or polarity, it is necessary to separately provide a deflecting electrode and an electrostatic lens for converging in the case of deflecting charged particles. Consequently, at least two electrodes are required for deflecting and at least two electrodes are required for converging, for a total of four required electrodes. For this reason, there is a problem of increased manufacturing costs. Also, in a droplet ejection apparatus, there is also the possibility that the distance from the nozzles to the print medium may become longer and the droplet landing precision may decrease.